1. Field of the Invention
The present invention relates to an in-vehicle load control system, and more particularly, to a system for controlling a load (e.g., a load such as a stop lamp) mounted on a vehicle.
2. Description of the Related Art
In a vehicle, various types of loads are provided, which can be controlled by signals from a switch and a sensor. Loads, e.g., lamps such as a stop lamp (brake lamp), a headlamp and a tail lamp, various motors, a solenoid, and a heater are located dispersedly in various locations on a vehicle. Various switches and sensors for outputting signals to operate those loads are also located dispersedly in various locations on the vehicle.
In a vehicle, loads placed at various locations on the vehicle are connected to one another using wire harnesses, so that each of the loads can be controlled by signals from a switch, a sensor, and so on. The wire harness is configured by bundling a lot of wires such as electric wires.
Further, generally, the wire harness is configured so that the turning-on/off of a single load can be operated by a signal from a single switch or sensor. Accordingly, if the numbers of switches and loads to be mounted on a vehicle are increased, it is necessary to transmit each of signals through the wire harness. Thus, the number of wires configuring a wire harness is vast.
Moreover, e.g., if a switch is placed at a front portion of a vehicle, whereas a load to be controlled is placed at a rear portion thereof, a signal should be transferred over a relatively long distance. Accordingly, the overall length of a wire harness is long, and the weight thereof increases.
Thus, in order to reduce the number and the weight of electric wires configuring a wire harness, as disclosed in JP-A-9-226451, it is conducted to transmit a signal from a switch or the like by multiplex communication. JP-A-9-226451 also discloses that a backup signal line is provided in addition to a multiplex communication channel such that even if a malfunction or a trouble occurs in a signal multiplex communication system, a load can be controlled by a signal from a manual switch.
Moreover, JP-A-2000-16174 discloses a technique for driving, when the breaking of a lamp is detected, an alternate lamp as a backup in the case of braking an important lamp such as a turn signal lamp or a stop lamp.
Incidentally, the term “multiplex communication” means “transmitting plural types of signals or information using a single signal line”.